From whatis.com 9/18/2014
text is an input technology that facilitates typing on a mobile device
by suggesting words the end user may wish to insert in a text field.
Predictions are based on the context of other words in the message and the
first letters typed. Because the end user simply taps on a word instead of
typing it it out on a soft keyboard, predictive text can significantly speed
up the input process.
Apple has included a predictive text bar called QuickType in the iOS 8 release. QuickType has a machine learning component that allows the software to build custom dictionaries. This helps the software to remember such things as whether or not the end user uses slang when communicating with specific people and adjust its text predictions accordingly. Android introduced predictive text with the release of Jelly Bean 4.1 in 2012.
One of the earliest applications for predictive text was T9 (text on 9 keys). T9 made typing on mobile phones and other small devices easier than multi-tapping, which required the user to tap numbers up to four times to register letter characters. T9 improved the user experience by associating groups of letters on each phone key with words in a dictionary. Software in the device correlated sequences of key presses with words in the dictionary and prioritized predictions by frequency of use.
Although predictive text technologies are becoming increasingly sophisticated, the software is still notoriously error-prone. Erroneous predictive text input on Apple devices is sometimes referred to as the Cupertino effect. The name was inspired by the way early spell checkers would change the word cooperation to Cupertino, which just happens to be the city in California where Apple has its corporate headquarters.